Polyphenylene ether resins (hereinafter xe2x80x9cPPExe2x80x9d) are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Furthermore, the combination of PPE with other resins provides blends that result in additional overall properties such as chemical resistance, high strength, and high flow.
One technical obstacle to the development of such blends is the lack of compatibility between PPE and many resins. This lack of compatibility manifests itself often through very poor physical properties as well as delamination in molded parts. Methods have been developed to improve the PPE compatibility with many resins such as, for example, with polyesters and polyamides. One of the more effective methods involves functionalizing PPE to make functionalized PPE containing moieties such as acid, anhydride, epoxy, orthoester, and the like that are reactive with the other resin in the blend. It is believed that when the functionalized PPE is allowed to react with the other resin that relatively small amounts of copolymer between the resins are formed. The copolymer is believed to be in large part responsible for improved compatibility between the PPE and the other resin. Indications of improved compatibility include resistance to delamination, improved physical properties such as increased tensile and impact properties and a stabilized morphology between the blend component phases under static and/or low shear conditions.
Methods to prepare functionalized PPE have included solution functionalization with an acid halide containing compound, such as trimellitic anhydride acid chloride, to make an endcapped PPE containing at least one reactive moiety such as acid, anhydride, epoxy, orthoester, and the like. This method is rather limited in the variety of functionalized PPE that can be made. Also, the by-products from the capping reaction tend to cause emulsion and/or isolation issues in the solvent precipitation stage of the process.
Another known method to prepare functionalized PPE related to melt functionalization of the PPE in an extruder. This method involved melting and mixing PPE with a functionalizing agent to result in a functionalized PPE. The functionalizing agent is typically a compound containing a carbon-carbon double or triple bond and one of the aforementioned reactive moieties and is believed to react through the unsaturated bond to functionalize the PPE. Additional polymers could be fed into the same extruder or alternatively, the functionalized PPE could be isolated and subsequently used to prepare other compositions. Melt functionalization has issues, such as difficulty in feeding PPE into the extruder due to low bulk density and wide particle size distribution. Moreover, PPE are often powders and require special handling to avoid potential dust explosion.
As explained above, the methods known in the art teach functionalization of the PPE with reactive groups such as acid, anhydride, epoxy, orthoester, and the like. However, for blending PPE with resin systems that involve curing or polymerization reactions, including radical reactions, it would be highly desirable to have a PPE that contained residual aliphatic unsaturation and capped phenolic end groups at the same time. Incorporation of unsaturated species onto the PPE to result in an olefinic functionalized PPE may allow for chemical grafting to occur between the olefinic functionalized PPE and the other unsaturated species that are being polymerized. Moreover, the hydroxyl groups that exist on PPE may interfere with radical polymerization reactions of unsaturated monomers and lead to undesirable low polymerization rates of the unsaturated monomer species.
PPE known in the art typically are of fairly high molecular weight for blending in the melt phase with other polymers and generally have in excess of 50 repeat monomer units, most often in excess of 80 or more repeat monomer units. Consequently, functionalization reactions and isolation methods have been developed for high molecular weight PPE. Although many physical properties, such as tensile properties, are enhanced with the high molecular weight of the PPE in the polymeric blend, in other new resin blend compositions, such as, for example, the polymerization of vinyl-substituted aromatic monomers, the high viscosity of the PPE having more than 50 repeat monomer units is undesirable as it presents difficulty with mixing. Additionally, the overall number of available endgroups available for chemical modification becomes fairly limited as the molecular weight increases.
For blending PPE with resin systems that involve curing or polymerization reactions, including radical reactions, it would be highly desirable from the standpoints of low viscosity for mixing and a high endgroup number for functionalization to have a PPE that contained residual aliphatic unsaturation and that has less than 50 repeat monomer units on average, preferably less than about 35 repeat monomer units on average. It is therefore apparent that a need continues to exist for novel and improved methods to prepare functionalized PPE containing residual aliphatic unsaturation, especially low molecular weight PPE (i.e. PPE having an intrinsic viscosity less than about 0.30 dl/g as measured in chloroform at 30xc2x0 C.).
The needs discussed above have been generally satisfied by the discovery of a process for preparing functionalized PPE containing aliphatic unsaturation. In one embodiment, the process comprises oxidative coupling in a reaction solution at least one monovalent phenol species using an oxygen containing gas and a complex metal catalyst to produce a PPE; and functionalizing the PPE, preferably prior to and/or during at least one isolation step for devolatilization of the reaction solvent, with an unsaturated compound of the formula (I): 
wherein R1 is an aliphatic or aromatic residue, for example, xe2x80x94CH2xe2x80x94 but may be multiple xe2x80x94CH2xe2x80x94 groups, e.g., n can vary from 1 to about 10 or more, or alternatively, n may equal zero wherein the formula is an acrylic residue, and wherein each of R2, R3, and R4 are independently hydrogen, alkyl, or aryl, and wherein X is a residue of one of the following formulae (II): 
or wherein X is a halogen or a residue of the formula (III): 
wherein R7 is an aliphatic or aromatic residue, for example, xe2x80x94CH2xe2x80x94 but may be multiple xe2x80x94CH2xe2x80x94 groups, e.g., m can vary from 1 to about 10 or more, or alternatively, m may equal zero (wherein if n and m both equal zero, the unsaturated compound is an acrylic anhydride), and wherein each R8, R9, and R10 are independently hydrogen, alkyl, or aryl. In a preferred embodiment, the unsaturated compound is of the formula (IV): 
wherein each of n, R1, R2, R3, and R4 are as previously described. In an especially preferred embodiment, the unsaturated compound is of the formula (V): 
The description that follows provides further details regarding various embodiments of the invention.
One embodiment of this invention provides for a process for the preparation of functionalized PPE containing aliphatic unsaturation, preferably having an intrinsic viscosity between about 0.08 dl/g and 0.60 dl/g, more preferably between about 0.10 dl/g and about 0.30 dl/g, by oxidative coupling at least one monovalent phenol species, preferably at least a portion of which have substitution in at least the two ortho positions and hydrogen or halogen in the para position, using an oxygen containing gas and a complex metal-amine catalyst, preferably a copper (I)-amine catalyst, as the oxidizing agent and, preferably extracting at least a portion of the metal catalyst as a metal-organic acid salt with an aqueous containing solution, and functionalizing the PPE with the addition of at least one unsaturated anhydride of the formula (I) prior to and/or during at least one isolation step for removal of the reaction solvent. In one embodiment, the functionalization is at least partly done in a flash process to concentrate the PPE reaction solution. In another embodiment, the functionalization is at least partly done prior to a flash process to concentrate the PPE reaction solution. In yet another embodiment, the functionalization is at least partly done in a devolatilizing extruder. The functionalization reaction is preferably done in the presence of at least one catalyst, preferably an amine-type catalyst. These and other embodiments will become apparent in the description that follows.
The PPE employed in the present invention are known polymers comprising a plurality of structural units of the formula (VI): 
wherein each structural unit may be the same or different, and in each structural unit, each Q1 is independently halogen, primary or secondary lower alkyl (i.e., alkyl containing up to 7 carbon atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or halohydrocarbonoxy wherein at least two carbon atoms separate the halogen and oxygen atoms; and each Q2 is independently hydrogen, halogen, primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbonoxy as defined for Q1. Most often, each Q1 is alkyl or phenyl, especially C1-4 alkyl, and each Q2 is hydrogen.
Both homopolymer and copolymer PPE are included. The preferred homopolymers are those containing 2,6-dimethyl-1,4-phenylene ether units. Suitable copolymers include random copolymers containing such units in combination with (for example) 2,3,6-trimethyl-1,4-phenylene ether units. Also included are PPE containing moieties prepared by grafting vinyl monomers or polymers such as polystyrenes and elastomers, as well as coupled PPE in which coupling agents such as low molecular weight polycarbonates, quinones, heterocycles and formals undergo reaction in known manner with the hydroxy groups of two poly(phenylene ether) chains to produce a higher molecular weight polymer, provided a substantial proportion of free OH groups remains.
The molecular weight and intrinsic viscosity of the PPE can vary widely, depending at least in part on the intended end-use for the PPE. The intrinsic viscosity (hereinafter xe2x80x9cI.V.xe2x80x9d) of the PPE is most often in the range of about 0.08-0.60 dl./g., preferably in the range of about 0.10-0.49 dl./g., more preferably in the range of about 0.10-0.30 dl./g., as measured in chloroform at 25xc2x0 C. In one especially preferred embodiment, the PPE has an I.V. in the range of about 0.10-0.25 dl./g. One unexpected aspect of the process is the ability to utilize a very wide range of I.V.
The PPE are typically prepared by the oxidative coupling of at least one monohydroxyaromatic compound such as 2,6-xylenol, 2,3,6-trimethylphenol, or mixtures of the foregoing by methods known in the art. Catalyst systems are generally employed for such coupling and they typically contain at least one heavy metal compound such as a copper, manganese, or cobalt compound, usually in combination with various other materials.
It will be apparent to those skilled in the art from the foregoing that the PPE contemplated in the present invention include all those presently known, irrespective of variations in structural units or ancillary chemical features.
The functionalizing agents used in the present invention to introduce the aliphatic unsaturation onto the PPE are unsaturated compounds of the formula (I): 
wherein R1 is an aliphatic or aromatic residue, for example, xe2x80x94CH2xe2x80x94 but may be multiple xe2x80x94CH2xe2x80x94 groups, e.g., n can vary from 1 to about 10 or more, or alternatively, n may equal zero wherein the formula is an acrylic residue, and wherein each of R2, R3, and R4 are independently hydrogen, alkyl, or aryl, and wherein X is a residue of one of the following formulae (II): 
alternatively, X may be a halogen or may be a residue of the formula (III): 
wherein R7 is an aliphatic or aromatic residue, for example, xe2x80x94CH2xe2x80x94 but may be multiple xe2x80x94CH2xe2x80x94 groups, e.g., m can vary from 1 to about 10 or more, or alternatively, m may equal zero (wherein if n and m both equal zero, the unsaturated compound is an acrylic anhydride), and wherein each R8, R9, and R10 are independently hydrogen, alkyl, or aryl. In a preferred embodiment, the unsaturated compound is of the formula (IV): 
wherein each of n, R1, R2, R3, and R4 are as previously described. In an especially preferred embodiment, the unsaturated compound is of the formula (V): 
However, included within the scope of the present invention are xe2x80x9cmixedxe2x80x9d or xe2x80x9cunsymmetricalxe2x80x9d anhydrides of formula (IV).
Although not wishing to be bound by any theory on the nature or mechanism of the chemical reaction between the PPE and the unsaturated compound of formula (I), it is presumed that the functionalization of the PPE takes place through the hydroxyl groups on the PPE resulting in a PPE containing aliphatic unsaturation comprising the formula (VII): 
each of Q1, Q2, n, R1, R2, R3, and R4 is as previously defined and j comprises a range of values generally on average between about 10 and 110 depending in large part on the I.V. of the PPE. In one embodiment, j has an average value less than 49. In another embodiment, j has an average value less than 34. In a preferred embodiment, the PPE containing aliphatic unsaturation comprises the formula (VIII): 
each of n, j, R1, R2, R3, and R4 is as previously defined. In an especially preferred embodiment, n is zero, R2 is CH3 or hydrogen and both of R3 and R4 are hydrogen. There can also be multiple aliphatic unsaturation introduced onto the PPE through incorporation of branching agents and/or coupling agents into the PPE backbone structure such that more than one end of the PPE contains hydroxyl groups for capping. Such branching agents and/or coupling agents are known in the art and include compounds such as, for example, tetramethylhydroquinone and trishydroxyphenol.
The functionalization reaction is preferably performed in a solvent, preferably in the polymerization reaction solvent. Suitable solvents are disclosed in the above-noted Hay patents. Aromatic solvents such as benzene, toluene, ethylbenzene, xylene, and o-dichlorobenzene are especially preferred, although tetrachloromethane, trichloromethane, dichloromethane, 1,2-dichloroethane and trichloroethylene may also be used.
One unexpected advantage of the present process when used to make functionalized low I.V. PPE is that a higher solids loading is possible as compared to processes that make higher (i.e.  greater than 0.28 I.V.) PPE. Without the increased solution viscosity build that concomitantly accompanies high molecular weight polymer, the final solids concentration can be increased by at least 20%, with increases of 30% or more possible. Thus, the present process affords a method for increased reactor utilization and productivity without increasing the size or number of the reactor vessels.
The temperature to carry out the functionalization stage of the invention generally ranges from about 20xc2x0 C. to about 100xc2x0 C., although higher temperatures are also possible. More preferably, the temperature range is from about 45xc2x0 C. to about 80xc2x0 C. At substantially higher temperatures, side reactions can occur leading to reaction by-products. One unexpected advantage of the present process is the relatively low temperatures that can be utilized and still achieve high levels of functionalization at acceptable reaction times.
After removal of the catalyst, the PPE containing solution is concentrated to a higher solids level as part of the isolation of the PPE. It was unexpectedly found that PPE can be readily functionalized to a PPE containing aliphatic unsaturation prior to and/or during this solvent removal process by addition of at least one functionalizing agent of the formula (I). The location of the addition of the at least one functionalizing agent will depend on several factors such as the stability of the agent, the volatility of the agent to the isolation conditions, the flexibility of the equipment for addition points, and the like. For functionalizing agents that are volatile in the isolation process, addition of the functionalizing agent prior to solvent removal is often preferred so as not to remove the functionalizing agent before it has functionalized the PPE. For less volatile functionalizing agents, greater flexibility in the location of the addition is possible. It is also possible to add functionalizing agent at several points during the process.
The amount of the above mentioned functionalizing agents that is required to appropriately functionalize the PPE is that which is sufficient to improve the compatibility between the various components in the final composition, i.e. between the PPE and the other resins and composite formulations, e.g., unsaturated polyesters, acrylics, and thermoplastics such as polyolefins. As previously discussed, indications of improved compatibility include resistance to delamination, improved physical properties such as increased tensile and impact properties and a stabilized morphology between the blend component phases under static or low shear conditions. For the most part, it is desirable for all hydroxy end groups on the PPE to be capped by the method of this invention. However, the invention includes compositions which contain a proportion of uncapped PPE; that is, PPE containing terminal hydroxy groups.
An effective amount of the above mentioned unsaturated compounds, based on the amount of the PPE, is generally up to about 3 molar equivalents, and is preferably up to about 2 molar equivalents, most preferably up to about 1.2 molar equivalents, all based upon the amount of terminal hydroxyl groups on the PPE as determined by FT-IR, usually in carbon disulfide. The actual amount utilized will also depend on, for example, the reactivity of the unsaturated functionalizing agent with the PPE hydroxyl groups, the catalyst employed, the reaction conditions, and the degree of capping that is desired in the PPE.
The capping efficiency and rate are improved by the addition of at least one catalyst. Although a wide variety of catalysts are useful, a particularly useful group of catalysts include the tertiary amines. It was unexpectedly found that 4-dialkylaminopyridines, such as 4-dimethylaminopyridine, as well as 4-pyrrolidinopyridine are especially useful for achieving high conversions at short reaction times under mild conditions as compared to other tertiary amines. The amount of catalyst can vary widely, however, the amount is generally an amount effective to improve the degree of conversion under a given set of reaction conditions as compared to the degree of conversion under the same conditions without the catalyst. Useful amounts generally range from about 0.1% by weight to about 10% by weight, preferably from about 0.5% by weight to about 5% by weight based on the amount of the PPE. An exact amount can be readily determined by statistical analysis under the reaction conditions, including the actual functionalizing agent reactivity, the reaction conditions, the equipment available, and the like without undue experimentation.
The functionalized PPE may be isolated in a variety of ways, including precipitation methods and total isolation methods. A total isolation process is often preferred for isolating the functionalized PPE when the I.V. is less than about 0.25 dl/g as measured in chloroform at 25xc2x0 C. As part of the total isolation, a portion of the solvent is preferably removed in order to reduce the solvent load on the total isolation equipment. Concentration of the PPE containing solution is preferably accomplished by reducing the pressure in a solvent flash vessel while preferably increasing the temperature of the PPE containing solution. Pressures of about 35 to 50 bar are desirable with solution temperatures increased to at least 200xc2x0 C., preferably of at least 230xc2x0 C. A solids level of PPE of at least 55%, preferably of at least 65% or higher is desirable.
The unsaturated functionalizing agent can be effectively added to the PPE at several locations during the isolation process. For example, functionalizing agent may be added prior to removal of solvent, the functionalizing agent may be added during the concentration of the reaction mixture, or both. Likewise, functionalizing agent can be added with the concentrated reaction solution into the final devise for solvent removal. Functionalizing agent may alternatively be added simultaneously at several different locations. The selection of the addition location may be dictated by the actual equipment utilized and by the properties of functionalizing agent with a determination of an optimum location.
For total isolation processes, the final isolation of the functionalized PPE is preferably carried out in a devolatilizing extruder although other methods involving spray drying, wiped film evaporators, flake evaporators, and flash vessels with melt pumps, including various combinations involving these methods are also useful and in some instances preferred. As previously described, total isolation is preferable from the viewpoint that oligomeric species are not removed to the same degree as with precipitation. Likewise, isolation yields are extremely high and are near quantitative. In these techniques it is highly preferred that the PPE polymerization catalyst (i.e. metal catalyst) removal be completed in the prior process steps as any metal catalyst remaining in solution will necessarily be isolated in the PPE.
Devolatilizing extruders and processes are known in the art and typically involve a twin-screw extruder equipped with multiple venting sections for solvent removal. The devolatilizing extruders most often contain screws with numerous types of elements adapted for such operations as simple feeding, devolatilization and liquid seal formation. These elements include forward-flighted screw elements designed for simple transport, and reverse-flighted screw and cylindrical elements to provide intensive mixing and/or create a seal. Particularly useful are counterrotating, non-intermeshing twin screw extruders, in which one screw is usually longer than the other to facilitate efficient flow through the die of the material being extruded. Such equipment is available from various manufacturers including Welding Engineers, Inc.
In the practice of one embodiment of the present invention, the preheated concentrated solution containing the functionalized PPE is fed into the devolatilizing extruder and maintained at a temperature less than about 300xc2x0 C., and preferably less than about 275xc2x0 C., with pressures in the vacuum vent of less than about 1 bar. The exact temperature will depend in large part on the I.V. of the functionalized PPE and the corresponding viscosity associated with that I.V. resin. It is noted that the functionalizing agent may alternatively be added at various locations along the length of the extruder with good results. The resultant solvent level is preferably reduced to less than about 1200 ppm, preferably less than about 600 ppm, and most preferably less than about 400 ppm.
Another unexpected result obtained through the use of a devolatilizing extruder was the extremely high yield of PPE achieved in the process. For example, a PPE yield of over 99% was obtained even for PPE having a low I.V. (typically on the order of about 0.08 dl/g to about 0.25 dl/g) whereas in the precipitation process known in the art, the yield of similar low I.V. PPE was less than 90%. Thus, the present process comprising a devolatilizing extruder affords a method to prepare functionalized low molecular weight polyphenylene ether resin containing aliphatic unsaturation, typically within the intrinsic viscosity range of about 0.08 dl/g to about 0.25 dl/g, in a yield of over 90%, preferably over 95%, more preferably over 98% and most preferably over 99%, based upon the amount of monovalent phenol utilized in the oxidative coupling.
When using a devolatilization extruder for the total isolation of the low I.V. functionalized PPE as previous described, it was found that traditional underwater or water spray cooling of strands of extrudate followed by chopping the extrudate into pellets gave unacceptable results presumably due to the low melt strength and inherent brittle nature of low I.V. PPE. It was found that special pelletization techniques can overcome these difficulties. Useful techniques include die-face pelletization, including underwater pelletization and flaking, declining angle strand pelletization using water spraying, and vibration drop pelletization with underwater pelletization especially suitable.
The collected PPE pellets can be dried using techniques standard in the art including centrifugal dryers, batch or continuous oven dryers, fluid beds, and the like. Determination of an appropriate set of conditions can be readily determined by one of skill in the art without undue experimentation.
As an alternative to completely isolating the functionalized PPE, one or more resins may be added to the devolatilized functionalized PPE in the same process. The one or more resins may be fed into the devolatilizing extruder although additional extruders may also be used. Possible variations include melt feeding the one or more resins into the devolatilizing extruder or melt feeding the functionalized PPE from the devolatilizing extruder into a second compounding extruder as well as combinations of these. Accordingly, in one embodiment a compatibilized blend is afforded by the process without complete isolation of the functionalized PPE. The one or more resins can vary widely and can also include additives common to such compatibilized blends. Such additives include impact modifiers, lubricants, flame retardants, pigments, colorants, fillers, reinforcing agents, carbon fibers and fibrils, and the like. Preferred resins include polyamides, polyesters, polyarylene sulfides, polycarbonates, polyetherimides, polyarylenes, functionalized polyolefins, polysulfones, polyethersulfones, and the like.
The functionalized PPE containing aliphatic unsaturation is especially useful in composite systems that involve a curing or polymerization step of unsaturated species, for example, styrene or acrylic-type monomers. It is believed that the aliphatic unsaturation introduced onto the PPE affords a reaction path to chemically link the PPE into composite system. Moreover, many of these same composite systems cure or polymerize, at least in part, through radical reactions. Uncapped PPE contains phenyl hydroxyl moieties that interfere with such radical reactions. In one embodiment, the functionalized PPE containing aliphatic unsaturation has the free hydroxyl groups xe2x80x9ccappedxe2x80x9d reducing the interference. By xe2x80x9ccappedxe2x80x9d is meant that at least about 80%, preferably at least about 90%, more preferably at least about 95% or more of the hydroxyl groups of the PPE have been reacted. It should be clear that the present invention also includes reaction products between the PPE containing aliphatic unsaturation and composite systems that involve a curing and/or polymerization step of unsaturated species. It should also be clear that the PPE containing aliphatic unsaturation is useful with a wide range of thermosetting resins, including but not limited to those selected from the group consisting of epoxy, phenolic, alkyds, polyester, polyimide, polyurethane, mineral filled silicone, bis-maleimides, cyanate esters, vinyl, and benzocyclobutene resins and can react in a variety of pathways with such resins.
All patents cited by reference are incorporated herein by reference.
In order that those skilled in the art will be better able to practice the invention, the following examples are given by way of illustration and not by way of limitation.